1. Field of the Invention
The present invention relates to a method of compressing and decompressing I/Q sample data in a cloud radio access network (CRAN), and more particularly, to a method of compressing and decompressing I/Q sample data in the CRAN that uses a fixed compression ratio and also determines a bit to be removed according to a magnitude of an absolute value of the I/Q sample data when compressing and decompressing I/Q sample data transmitted and received between a digital unit (DU) and an radio unit (RU) in the CRAN.
2. Discussion of Related Art
Recently, a centralized/cloud radio access network (CRAN) structure has been widely introduced into base station systems. In the CRAN structure, a digital unit (DU) and radio unit (RU) of a base station system are separately implemented in order to reduce capital expenditure (CAPEX) and operational expenditure (OPEX) and also secure efficiency in the development of an apparatus.
In the CRAN, typically, DUs are mainly positioned in a DU center provided in a telecommunication office while RUs are installed in a service area that is spaced apart from the DU center. For high-speed transmission and reception of baseband I/Q signals, DUs and RUs are physically connected by an optical link or unshielded twisted pair (UTP) cable.
At present, one of the standards that is most widely used to transmit and receive I/Q data between the DU and RU is a common public radio interface (CPRI). Further, Version 6.0 of the standard may support a maximum line bit rate of 10,137.6 Mbps.
A standard similar to the CPRI includes an open baseband remote radiohead interface (OBSAI) that is defined prior to the CPRI and an open radio interface (ORI) that is a lower standard. For convenience, the CPRI standard will be described below as an example. However, naturally, the OBSAI and ORI are not excluded.
FIGS. 1A and 1B show several connection forms that can be supported by the CPRI standard. FIG. 1A shows the simplest configuration in which one radio equipment control (REC) corresponding to the DU and one radio equipment (RE) corresponding to the RU are connected by a single CPRI link. Further, one REC and one RE may be connected by a plurality of CPRI links. FIG. 1B shows a star topology configuration in which one REC and a plurality of REs are connected by one or more CPRI links.
According to the CPRI standard, various configurations such as a chain topology, tree topology, or ring topology other than the described-above configuration may be used to connect the REC and the RE. In the CPRI standard, no method for compressing data is defined. Hereinafter, in the standard, the term “node” is used to refer to any one subsystem implemented in the REC and RE.
Korean Patent Application No. 10-2013-0052642 entitled “Method of Compressing and Decompressing I/Q Data between a DU and RU in a CRAN” (hereinafter referred to as an “earlier filed invention”) was filed on May 9, 2013 by the applicant.
In the earlier filed invention, a technology is disclosed that can significantly reduce an amount of data transmitted and received between the DU and RU by setting a basic unit of compression as a group of basic frames defined in the CPRI standard, defining a header including information about a remaining amount of data, and transmitting or receiving the header for each basic unit of compression. The earlier filed invention may include setting a basic unit of compression as a basic frame group consisting of a plurality of unit blocks, performing compression at a compression ratio decided independently for each unit block, collecting a header containing information about the compression ratio of each unit block, performing Huffman encoding on the header, and transmitting the header to another party node.
However, the earlier filed invention has a limitation in that compression efficiency is low because header information is added to respective unit blocks.
Furthermore, the earlier filed invention also has other limitations in that implementational complexity is high when hardware is designed using a register transfer language (RTL) because the number of transfer bits of I/Q sample data is variably set for each unit block, and a large amount of calculation should be performed in a short time because a header for each unit block is collected and then Huffman encoded for each basic unit of compression when the I/Q sample data is compressed.